Remote indicators are useful in a wide variety of monitoring applications where it is desired to angularly display measured data at one or more locations remote from the point of measurement. The data can be inherently angular in nature, such as compass bearings, or it can be data, such as pressure, which is related to angular display only by calibration on a circular dial. On a large ship, for example, it may be desirable to transmit and display at several locations, the compass heading determined to a single properly-compensated, highly accurate compass; and where a ship tows a barge or another ship, it is highly desirable to transmit to the towing ship, the leading of the barge or ship being towed.
Typical prior art remote indicators utilize stepping motors with step-driven coils to displace a magnetic indicating rotor. These devices, however, suffer from a number of disadvantages. One such disadvantage is that their accuracy is typically limited by the resolution of the stepping motor. Thus an indicator employing a 7.5.degree. stepping motor is typically limited in accuracy to .+-.3.75.degree.. Although gearing can be added to reduce the step increments, this technique is considerably less reliable than the direct drive approach utilized in this invention. Higher resolution stepping motors are available, but their cost, complexity and size rise rapidly with increasing resolution.
A second difficulty arises because of residual magnetism. Because the magnetic fields do not completely dissipate upon the withdrawal of current, the motor does not accurately respond to a fast changing signal, introducing errors in accuracy.
Accordingly, it is desirable to provide an economical remote indicator capable of providing more accurate angular display of transmitted data.